iPitomy is a on premise solution that is "Asterisk" base in the backend. The PBX is a bare bones style PBX which makes for a simple yet easy to manage phone system.
When adding new networks/remote locations to the iPitomy Phone system you need to add the following;
System -> Access Control -> Access Control List; Make sure to add x.x.x.x/255.255.255.0 (subnet) Example would be 10.10.3.0/255.255.255.0
This will add the entire network of 10.10.3.0/24. You will also need to add this to the PBX setup located at;
PBX Setup -> SIP -> Local Networks and Subnet Masks:
This will grant all the pbx phones in the remote location of 10.10.3.0/24. I suggest that you use a managed switch and setup vlan with trunking of LLDP so that the phones are on their own network and not using up ip space. IPv6 will be a bit different as you're dealing with 64bit addresses.
Phone not registering, entering a forbidden state;
This is due to some sort of access issue, could be related to the firewall, wrong ACL or a password problem. To change the password on the phone you can go to the IP of that phone input the username/password (default is: root:root) and change the password located in;
SIP Account -> Account1 -> Basic Authenticate Name:xxxx Password: xxxx
Double check that the auth/password on the server is identical:
Destinations -> Extensions -> Items/Edit PBX Settings for Extensions X -> Advanced -> SIP Password